1. Field of the Invention
This invention relates generally to communication systems and more particularly to a diversity system and method of data communication using signal delay diversity combined with communication signal phase and/or amplitude diversity associated with TDMA and CDMA communication signals among others.
2. Description of the Prior Art
Delay diversity is a method of transmit antenna diversity in which the same signal is transmitted from multiple antennas, with each antenna having a different time delay. Delay diversity was introduced for TDMA systems such as IS-54 and GSM (global system for mobile communications) by N. Seshadri and J. Winters, Two Signaling Schemes for Improving the Error Performance of Frequency-Division-Duplex (FDD) Transmission Systems Using Transmitter Diversity, Vehicular Technology Conference, pp. 508-511 (1993) and A. Wittneben, A New Bandwidth Efficient Transmit Antenna Modulation Diversity Scheme for Linear Digital Modulation, International Communications Conference, vol. 3, pp. 1630-1634 (1993), wherein the delays for each antenna are chosen to be a multiple of the symbol interval. Present TDMA systems are characterized by transmission of different data signals over a common channel by assigning each signal a unique time period. These data signals are typically transmitted as binary phase shift keyed (BPSK), Gaussian minimum shift keyed (GMSK), or quadrature phase shift keyed (QPSK) data symbols during such unique time periods. These unique periods are allocated to a selected receiver to determine the proper recipient of a data signal. Allocation of such unique periods establishes a communication channel between a transmitter and selected remote receivers for narrow band transmission. This communication channel may be utilized for cable networks, modem transmission via phone lines or for wireless applications.
A selected TDMA receiver must determine both carrier phase and symbol timing of its unique period from the received signal for data recovery. The carrier phase is necessary for generating a reference carrier with the same phase as the received signal. This reference carrier is used to coherently demodulate the received signal, thereby creating a baseband signal. Symbol timing synchronization of the receiver with the transmitter is necessary for the receiver to extract correct data symbols from the baseband signal.
Delay diversity for a synchronous CDMA system (IS-95) was disclosed in U.S. Pat. No. 5,781,541, entitled CDMA System Having Time-Distributed Transmission Paths for Multipath Reception, by A. Schneider, issued Jul. 14, 1998 wherein the delays for each antenna are greater than a chip interval and less than the base station sequence offset between base stations. The Seshadri et al., Wittneben and Schneider references are incorporated by reference herein. Delay diversity for another CDMA communication system and using a distributed antenna system to provide multipath signals in order to facilitate signal diversity for enhanced system performance was disclosed by Gilhousen, et al. in U.S. Pat. No. 5,280,472, entitled CDMA Microcellular Telephone System and Distributed Antenna System Therefor, issued Jan. 18, 1994. A communication system having the advantages of delay diversity in combination with phase and/or amplitude diversity is however, presently unknown. In view of the above, a wireless communication system having selectively variable transmit antenna delays or signal delays combined with selectively variable transmitted signal amplitudes and/or phase characteristics to accommodate TDMA and CDMA modes of communication among others, is both advantageous and desirable to further optimize signal reception.